Help with understanding if leds and voltage can change on a basic circuit

I have had a search but couldn't find what i needed. My skills are pretty limited, hence my asking.

I'm also not asking for anyone to do this for me, i'm just looking for a point in the right direction really and hopefully i can do the research when i know what to look at to get the job done.

ultimately i am looking to improve this wireless brake light, its running 3v worth of LEDs but i would like it to run 12v LEDs...

So, i have found one of these wireless brake and indicator lights which fit on your helmet on ebay, the transmitter part looks good but the leds look pretty weak, probably not much use in the day time. (please see link below)

i am thinking putting the circuit in a little box to protect it, attach the light strip to the back of my jacket with a 12v battery pack of 8xAA batteries in a pocket to power it. and perhaps add a couple more indicators to have them further apart on my shoulders. this is in the interest of safety after all, not fashion!

is it possible just to unsolder the original LEDs and splice in the new ones and power them off the battery pack? im guessing not, thats why i ask...